Removes exception is sysctl file is missing

When syscl file was missing, sysctl module was complaining about it and
bailing out.
This behaviour prevents usage of /etc/sysctl.d directory, present in
some distributions.
This patch accepts a missing sysctl.conf file so sysctl.d directory can
be used.
However, it will bail out if the destination directory doesn't exist.
Changed when new sysctl file is created

When destination sysctl file is missing, it is created.
But, for idempotency purposes, the creation process now takes place just before it is used, in the
main code path so an empty file is not left over if the code
module.fail_jsons before the file is really used.
Removes useless empty string write

It s not necessary to write an empty string for the file to be created.
Merge pull request #2145 from leucos/sysctl_no_file_check

Better sysctl module file check